This invention relates to a control system for a construction machine such as a hydraulic excavator, said control system being provided with a controller for controlling an engine speed and a maximum pump absorption torque.
As a conventional technique of this type, there is one disclosed in JP-A-07119506. The control system according to this conventional technique is, for example, for a hydraulic excavator having an engine, a variable displacement hydraulic pump driven by the engine, a pump regulator for controlling a delivery rate of the hydraulic pump, a fuel injection system, i.e., governor for the engine, hydraulic actuators such as travel motors and an arm cylinder driven by pressure oil delivered from the hydraulic pump, flow control valves such as travel control valves and arm control valve for controlling flows of pressure oil to be supplied from the hydraulic pump to the hydraulic actuators, and control levers such as an arm lever for controlling these flow control valves, in other words, control devices. The control system is provided with a controller, which includes an engine speed control means for correcting an existing target engine speed in accordance with a stroke of the control lever to obtain a new target engine speed and a pump absorption torque controlling means for determining a target value of maximum pump absorption torque corresponding to the above-described new target engine speed.
This conventional technique detects a stroke of the control lever and a load on the hydraulic pump, and corrects a target engine speed in accordance with the stroke and load. Described specifically, the target engine speed is controlled to a lower target engine speed to achieve an energy saving when the stroke of the control lever is small and the load is low, and the target engine speed is controlled to a higher target engine speed to achieve an improvement in the efficiency of work when the stroke of the control lever is large and the load is high.
A construction machine such as the above-described hydraulic excavator is, however, accompanied by a potential problem that, when the construction machine is continuously operated under high loads or the construction machine is arranged in a high-temperature environment, the temperature of an engine coolant may rise to result in overheating and the work performed by the construction machine may have to be discontinued. In the above-described conventional technique, however, avoidance of such overheating was not taken into consideration.
With the above-described potential problem of the conventional technique in view, the present invention has as an object the provision of a control system for a construction machine, which can achieve a saving in energy and an improvement in the efficiency of work and can also avoid overheating.
To achieve the above-described object, the present invention provides in a first aspect thereof a control system for a construction machine provided with an engine, a variable displacement hydraulic pump driven by the engine, a pump regulator for controlling a delivery rate of the hydraulic pump, a fuel injection system for the engine, hydraulic actuators driven by pressure oil delivered from the hydraulic pump, flow control valves for controlling flows of pressure oil to be supplied from the hydraulic pump to the hydraulic actuators, and control devices for controlling the flow control valves, said control system being provided with a controller including an engine speed control means for correcting a reference target engine speed, which is inputted by an operator, in accordance with a controlled amount of at least one of the control devices to obtain a corrected target engine speed and a pump absorption torque control means for determining a target maximum pump absorption torque value corresponding to the corrected target engine speed, wherein the control system is provided with a coolant temperature detector for detecting a temperature of an engine coolant; and the controller comprises a first correcting means for correcting the corrected target engine speed, which has been obtained by the engine speed control means, and the target maximum pump absorption torque value, which has been computed by the pump absorption torque control means, into a new target engine speed and a new target maximum pump absorption torque, respectively, in accordance with the coolant temperature detected by the coolant temperature detector.
According to the invention of claim 1 constructed as described above, a rise in the temperature of the engine coolant as a result of continuous operation under high loads is detected by the coolant temperature detector. In accordance with the coolant temperature so detected, the first correction means corrects an existing corrected target engine speed into a new target engine speed within such a range that no overheating will be caused to occur, and at the same time, also corrects an existing target maximum pump absorption torque value into a new target maximum pump absorption torque commensurate with the new target engine speed.
By the above-described corrected target engine speed and target maximum pump absorption torque value, it is possible to achieve a saving in energy and an improvement in the efficiency of work as in the conventional technique, and moreover, it is also possible to surely avoid overheating in accordance with the above-described new target engine speed and target maximum pump absorption torque obtained by the first correction means.
The present invention, in a second aspect thereof, is characterized in that in the above-described first aspect of the present invention, the engine speed control means comprises a first correction value computing means for correcting the reference target engine speed in accordance with types of the hydraulic actuators and a computing means for determining the corrected target engine speed in accordance with the first correction value and the reference target engine speed; and the first correcting means comprises a second correction value computing means for determining a second correction value, which corrects the corrected target engine speed in accordance with a preset functional relation, based on the temperature of the coolant detected by the coolant temperature detector, a first engine speed computing means for determining a new target engine speed in accordance with the second correction value and the corrected target engine speed, a third correction value computing means for determining a third correction value, which corrects the target maximum pump absorption torque value in accordance with a preset functional relation, based on the coolant temperature detected by the coolant temperature detector, and a first torque computing means for determining a new target maximum pump absorption torque in accordance with the third correction value and the target maximum pump absorption torque value.
The present invention, in a third aspect thereof, is characterized in that in the above-described second aspect of the present invention, the engine speed control means comprises a fourth correction value computing means for determining a fourth correction value, which corrects the reference target engine speed, in accordance with operating directions of the hydraulic actuators; and the first engine speed computing means determines a still new target engine speed in accordance with the fourth correction value and the new target engine speed.
The present invention also provides in a fourth aspect thereof a control system for a construction machine provided with an engine, a variable displacement hydraulic pump driven by the engine, a pump regulator for controlling a delivery rate of the hydraulic pump, a fuel injection system for the engine, hydraulic actuators driven by pressure oil delivered from the hydraulic pump, flow control valves for controlling flows of pressure oil to be supplied from the hydraulic pump to the hydraulic actuators, and control devices for controlling the flow control valves,
said control system being provided with a controller including an engine speed control means for correcting a reference target engine speed, which is inputted by an operator, in accordance with a controlled amount of at least one of the control devices to obtain a corrected target engine speed and a pump absorption torque control means for determining a target maximum pump absorption torque value corresponding to the corrected target engine speed, wherein:
the control system is provided with a working oil temperature detector; and
the controller comprises a second correcting means for correcting the corrected target engine speed, which has been obtained by the engine speed control means, and the target maximum pump absorption torque value, which has been computed by the pump absorption torque control means, into a new target engine speed and a new target maximum pump absorption torque, respectively, in accordance with a working oil temperature detected by the working oil temperature detector.
According to the fourth aspect of the present invention constructed as described above, a rise in the temperature of working oil flowing through a hydraulic circuit of the construction machine as a result of continuous operation under high loads is detected by the working oil temperature detector. In accordance with the working oil temperature so detected, the second correction means corrects an existing corrected target engine speed into a new target engine speed within such a range that no overheating will be caused to occur, and at the same time, also corrects an existing target maximum pump absorption torque value into a new target maximum pump absorption torque commensurate with the new target engine speed.
By the above-described corrected target engine speed and target maximum pump absorption torque value, it is possible to achieve a saving in energy and an improvement in the efficiency of work as in the conventional technique, and moreover, it is also possible to surely avoid overheating in accordance with the above-described new target engine speed and target maximum pump absorption torque obtained by the second correction means.
The present invention, in a fifth aspect thereof, is characterized in that in the above-described fourth aspect of the present invention, the engine speed control means comprises a first correction value computing means for correcting the reference target engine speed in accordance with types of the hydraulic actuators and a computing means for determining the corrected target engine speed in accordance with the first correction value and the reference target engine speed; and the second correcting means comprises a fifth correction value computing means for determining a fifth correction value, which corrects the corrected target engine speed in accordance with a preset functional relation, based on the working oil temperature detected by the working oil temperature detector, a second engine speed computing means for determining a new target engine speed in accordance with the fifth correction value and the corrected target engine speed, a sixth correction value computing means for determining a sixth correction value, which corrects the target maximum pump absorption torque value in accordance with a preset functional relation, based on the working oil temperature detected by the working oil temperature detector, and a second torque computing means for determining a new target maximum pump absorption torque in accordance with the sixth correction value and the target maximum pump absorption torque value.
The present invention, in a sixth aspect thereof, is characterized in that in the above-described fifth aspect of the present invention, the engine speed control means comprises a fourth correction value computing means for determining a fourth correction value, which corrects the reference target engine speed, in accordance with operating directions of the hydraulic actuators; and the second engine speed computing means for determining a still new target engine speed in accordance with the fourth correction value and the new target engine speed.
The present invention, in a seventh aspect of thereof, is characterized in that in any one of the above-described first to sixth aspects of the present invention, the construction machine is a hydraulic excavator.